Blood contact with the wound and biomaterials of the cardiopulmonary bypass (CPB) system activates five plasma protein systems and five blood cells to produce cytotoxins and vasoactive chemicals and enzymes that mediate the bleeding, thrombotic and inflammatory complications of open heart surgery (OHS). The rationale of this proposal is that under- standing mechanisms of blood protein and cellular reactions during CPB and OHS identifies specific enzyme and activated cellular targets for temporary inhibition during the period of CPB. A specific hypotheses for selection of potential inhibitors is based on this knowledge of mechanisms. We use simulated extracorporeal circulation (SECC) for initial testing of potential inhibitors chosen from analysis of biochemical properties. The in vitro perfusion circuit consists of a 0.4M2 spiral coil membrane oxygenator, roller pump and reservoir bag to recirculate fresh heparinized human blood for 2-6 hours usually at 37 degrees C. We also use a baboon model that is being modified to include a subcutaneous tunnel to simulate a wound. The baboon is chosen since approximately 90 percent of human antibodies cross-react with baboon proteins and cells; thus the model that both robust and efficient. Previous work by ourselves and others have demonstrated the rationale of this approach in the use of fibrinolytics and proposed use of eptibatide for protecting platelets (see Progress Report). This project focuses on suppressing formation of the prothrombinase complex, complement activation and activation of neutrophils, monocytes and platelets. One goal is to inhibit thrombin formation. Prior studies indicate that inhibiting formation of the prothrombinase complex is necessary. We plan to study a tight binding new inhibitor of factor Xa, a factor IXai inhibitor and recombinant tissue factor pathway inhibitor individually and in combination. Suppression of neutrophil and monocyte activation focuses on cyclic AMP, cyclic GMP and specific phosphodiesterase inhibitors (PDEs). We will also study inhibition of neutrophil and monocyte Mac-1 receptor binding using synthesized peptides in an effort to inhibit cellular activation. Lastly we plan to study two potential inhibitors of complement activation that prevent cleavage of C3 by different means. Because blood reactions during CPB and OHS are often mutually interdependent, we plan to study combinations of inhibitors that we believe will act synergistically.